1. Field of the Invention
The present invention relates to an engine speed controlling apparatus for an internal combustion engine, and more particularly to an engine speed controlling apparatus for controlling the engine speed of an internal combustion engine mounted on an industrial vehicle such as a fork lift or on an internal combustion engine used as a power source such as a generator.
2. Description of the Related Art
In an internal combustion engine mounted on an industrial vehicle such as a fork lift or the like, since the cargo load acts in addition to the traveling load, it is necessary to prevent a change in the traveling load from hindering the loading and unloading operations and a change in the cargo load from hindering the traveling of the vehicle. In addition, an internal combustion engine used as a power source such as a generator is required to supply electric power on a stable basis. Various controlling apparatuses have hitherto been developed with a view to running such an internal combustion engine at a speed in the vicinity of a targeted engine speed. As one of such controlling apparatuses, a method is known in which the dynamics of the internal combustion engine and the load is approximated and expressed as a linear transmission function around a certain operating point of each factor, and compensation is effected through proportional plus integral plus differential (PID) action control (refer to "The Report of Experiments on the Speed Governing of Diesel Engine-Generator", Transactions of the Japan Society of Mechanical Engineers (Part 1) Vol. 43, No. 367, page 957, line 13 of the left column to line 1 of the right column).
With the above-described conventional art, however, since the control system is designed by using characteristics of the internal combustion engine around certain operating points, there arises a need to design the control system for each operating point and effect control by changing over to an operation expression for control with respect to each operating point in conjunction with changes in the operating region of the internal combustion engine. Accordingly, this results in a problem such as an increased number of processes involved in designing the control system, and hunting which occurs in the engine speed at the time of making a changeover for control due to the discontinuity in expressions for control calculation.